Visualizing the subsurface bending of vortex lattices under tilted magnetic fields in the isotropic superconductor β-Bi₂Pd.

In type-II superconductors vortices are quantized magnetic flux lines are usually oriented parallel to the magnetic field and tend to be straight to minimize their elastic energy. For many years, the orientation of vortices when the field is approximately parallel to a surface has been commonly overlooked, particularly for high values of the magnetic field. Here, we use scanning tunneling microscopy to study vortex lattices in the weak-pinning and nearly isotropic superconductor β-Bi₂Pd in tilted magnetic fields. We show that vortices exit the sample perpendicular to the surface, even when the magnetic field is parallel to the surface. Thus, vortices are bent beneath the surface. We analyze how the structure and orientation of the tilted vortex lattices in the bulk are strongly affected by Coulomb-type intervortex repulsion at the surface due to the stray (Pearl-like) magnetic fields [1].
[1] E. Herrera, et. al., Physical Review B, 96, 184502 (2017)